Multi-dose pharmaceutical formulations such as a nasal spray, or an otic or ophthalmic drop formulation, that contains a pharmaceutical active typically includes a preservative agent to inhibit growth of bacteria and/or fungi if the formulation becomes contaminated with such organisms. Such preservative agents should have a broad spectrum of preservative activity and be non-irritating to biological tissues. Many preservative agents, however, have a tendency to irritate such tissues, particularly, if the agent is present at relatively high concentrations.
In addition, many dermatological products including, but not limited to cosmetic formulations, also require the presence of a preservative or antimicrobial agent. Again, such preservative agents should have a broad spectrum of preservative activity and be non-irritating to the skin.
U.S. Pat. No. 5,578,598 describes the use of a water insoluble, polyelectrolyte complex that is prepared by mixing an aqueous solution of a cationic polymer and an aqueous solution of an anionic polymer. The cationic polymer includes quaternary ammonium polymers of formula A

wherein R1 and R4 are independently a C1-C10alkylene or a disubstituted C8-C10arylene; R2, R3, R4 and R5 are independently a C1-C3alkyl; and m is a number from 5 to 500. The corresponding anionic polymer includes a peptide with anionic acidic sites, an acrylic acid polymer or a biopolymer with anionic sites such as hyaluronic acid, alginic acid or chondroitin sulfate. The polyelectrolyte complex is obtained as a gelatinous precipitate from the aqueous solution. The polyelectrolyte complex is said to possess antimicrobial activity if applied as a coating to almost any material substrate.
Given the requirement of preservative agents or systems in many pharmaceutical formulations, and in particular, for multi-dose formulations, there remains an interest in identifying and developing such agents with a relatively robust antimicrobial activity and a relatively low toxicity profile.